1. Field of the Invention
The present invention relates to ballpoint pens which utilize refill ink cartridges, particularly the maintaining of ambient pressure in such ink cartridges.
2. Description of the Prior Art
It is known that, in ink cartridges of this type, the head space between the back of the cartridge and the upper level of the ink should be kept as close as possible to ambient pressure, in order to prevent a pressure drop during writing which would oppose proper ink flow, as well as to prevent overpressurization which would result in overfeeding of the ink supply.
Thus, it has been proposed that the backward portion of the cartridge be provided with an orifice designed to insure pressure communication with the ambient atmosphere. Such an arrangement is satisfactory when the ink is of relatively low volatility. However, when the cartridge contains a relatively volatile ink formula, ongoing evaporation results in overconsumption of the ink.
In view of this disadvantage it has been proposed that an orifice or orifices be provided at the forward portion of the refill, and that the orifice or orifices be made to communicate with the backward portion thereof by the provision of a duct inside the ink reservoir. However, such a construction only prevents overconsumption of the ink to the extend that the user replaces the pen cap after each use.